Since WWI the idea of the Schlieffen plan has dominated our view of the war. It proved German War guilt and militarism and made France and the allies seem like victims. The common theme in literature about WWI is that Moltke ignored the Schlieffen plan's "Strong Right Wing" approach meaning that the encirclement of Paris could not be completed.

There is no "German war guilt". All Versailles said was that Germany initiated hostilities against France and Belgium and occupied territory for 4 years -- it has nothing to do with guilt, it was to provide a legal backing for reparation and nothing more. It has nothing to do with "making France and the allies seem like victims". You should read the German treaty for Russia, Brest-Litovsk, or the treaties for Austria-Hungary and the Ottomans sometime. If you want to read what treaties sound like when a country is actually trying to destroy another on a piece of paper sounds like those are what you should read. Germany was kept pretty much in tact -- her industry was nearly untouched and remained the largest GDP on continental Europe. Fortunately for them the British went from largest creditor to largest debtor and needed a strong German economy.

a) Schlieffen's plan involves 24 nonexistent divisions

Hence why it was heavily modified by Moltke. It had an unrealistic expectation of men to be sent through Belgium.

b) The plan was written after Schlieffen's retirement

It was written and codified into the Aufmarsch I (Deployment Plan I) in 1905. He retired in 1906.

c) The Schlieffen plan was never tested in any War Games

It was not an operational plan, it was a deployment plan. That does not need to be tested. Regardless the original Schlieffen Plan was never taken into serious consideration because almost immediately after its adoption did the reality of an Ost, Eastern, war plan have to be taken into consideration. The Schlieffen Plan was an isolated Franco-German situation, it did not, at all, consider Russia's involvement. Thus it was never tested because Russia was always an actor.

d) East Prussia was left totally undefended

See above. It was a plan for a solely Franco-German War, hence why it was almost immediately adapted.

e) The actual plan was never official doctrine

Most war plans are not, that's why they're plans. The French went through like 6 plans in less than 10 years and none of them had actual war games to test them, yet we don't pretend the French Plan XVII didn't exist.

The existence of these inconsistencies raises the questions. Why was the Schlieffen plan written in the first place? and Why is the Schlieffen plan so widely acknowledged as an absolute truth?

Because even though the plan was never taken at its absolute face value its themes were. That France had to be knocked out fast. That a rapid advance through Belgium was necessary. That in every plan following it there existed a surplus of men in this 'swinging arm' going through Belgium. It was never actually implemented in any serious way but it set the tone of German military planning throughout. Yes Moltke's ultimate plan did not look like the Schlieffen Plan. The Netherlands was left alone, there was a 3:1 ratio of men in the swinging arm to men in Alsace-Lorraine compared to 7:1 in Schlieffen's original plan. East Prussia had a stout defense as well. However the deployment concepts remained the same -- flood men into Belgium, swing round hard, encircle the French. Repeat 1870.

The Schlieffen plan is so widely accepted because it neatly ties in with the Allied view of the war. Although it is an age old cliché the winners do indeed write history. Keen to put the blame on Germany the allies stated that Germany carried the war guilt due to its offensive in France. The Schlieffen plan conveniently fit this narrative exactly and so it was accepted as truth despite the aforementioned inconsistencies.

Are you here to actually discuss or are you here to stand on a pedestal and preach? This old saying needs to die right now because, of all cases, this is not the case where "the winners write history". This is the precise opposite. WWI is the most spectacular case of the losers writing history in, well, pretty much all of history. The narrative of 'everyone was equally responsible for the war' and 'Versailles placed all war guilt on Germany' (or any) and 'Versailles caused Hitler's rise and forced WWII to happen' is flat out propaganda from the mouths of the German Foreign Office. This is spelled out very concisely in the recently freed from JSTOR paper Clio Deceived: Patriotic Self-Censorship in Germany after the Great War by Holger Herwig. I'd really suggest reading this immediately after finishing this post.

Like this isn't conspiracy theory or nutters going off the deep end of "Allied propaganda". This is, flat out, the reality. Through intentional censorship of documents and thorough propaganda campaigns combined with an Anglosphere who was thoroughly done with war in the 20's and 30's who ate it all up and hated their governments for pushing them through it we got a totally skewed perspective of the war. A perspective which was only changed in the 1950's and especially the 1960's as we got first time access to uncensored documents in Germany because, well, we were occupying them. We got even more in the 1990's after the fall of the Soviet Union, especially from Austria-Hungary as well.

So in short: You saying "the winners write history" in this case is rather ironic considering it was the losers writing history that misled academia for 40 years and the public mind to this day. No, Versailles did not place war guilt upon Germany it said that Germany occupied France and owed reparations for said occupation. That is as standard as standard gets. The Schlieffen Plan wasn't codified law, it was never meant to be. It was, however, a theoretical plan that set the tone of German war planning for the next decade leading up to the war.

Other works if you're interested are The First World War: Germany and Austria-Hungary, 1914-1918 by Holger Herwig and The First World War: To Arms! by Hew Strachan. If you're really interested in history though you gotta get Fritz Fischer's legendary work German War Aims in the First World War -- it was published in 1961 and was the first academic work that used all the new data from the German archives we got after the war. While his analysis is not taken as strictly these days his research is absolutely legendary and turned academia on its head.

/u/elos_ has covered the problems with the interpretation of the Schlieffen Plan you presented; I'd like to cover a problem with the methodology itself. When examining the sources you provided, I was struck by this remark on the about page of terencezuber.com:

I seek to establish German military history according to the standard of Leopold von Ranke: "as it actually was."

A layman reading that might be thoroughly impressed by that sentence - a historian telling things as they actually were, that's what we need, right? To me that sentence indicates something else. It basically says he's ignoring the last 150 years of historiography - how historians "do" history.

Now don't get me wrong, Ranke was a very important person in historiography and many academics will prefer his stance on history over that of historians of earlier centuries - but there have been so many developments since Ranke, new methods explored, new insights gained. Furthermore, Ranke himself is often misunderstood.

As John Tosh puts it in The Pursuit of History:

Ranke's fame as the champion of rigorous source criticism has sometimes been allowed to obscure the emphasis that he laid on contemplation and imagination: 'after the labour of criticism', he insisted, 'intuition is required'. [p. 167]

That is to say, once you know what the source says 'actually' happened, the historian will still have to fit that into a narrative which has to be thought about. Even in Ranke's ideas of rigorous source criticism, the historian plays a pivotal role in presenting the history. The question is how good historians (or humans) are at presenting things objectively. Not so good, the modern consensus is:

Ranke's story thus contained an irreducibly fictive or creative element. His documents did not tell him when to start his story or when to end it. (...) To claim, as Ranke did - and as some historians still do - to be writing down 'what actually happened', no more and no less, is to fall victim to what an anthropologist (neatly turning the historians' use of the term 'myth' against them) has recently called 'the myth of realism' (...). In other words, the boundary between fact and fiction, which once looked firm, has been eroded (alternatively, it is only now that we see that the boundary was always open). [Burke, p. 125]

Proper philosophers have weighed in on this. Paul Ricoeur in his Time and Narrative has a chapter on "The interweaving of history and fiction". In it, he distinguishes between a 'dated past' (what happened), a 'reconstructed past' (what we think happened), and a 'refigured past' (how we create our narrative based on what we think happened). Now this is pretty heavy stuff, but just to give you a taste of it:

Once we have admitted that the writing of history is not something added from outside to historical knowledge but is one with it, nothing prevents us from admitting as well that history imitates in its own writing the types of emplotment handed down by our literary tradition. [p. 185]

Conclusion

To pull this back to your question. The fact that you or others choose to look solely at the Schlieffen Plan and how it was 'actually' not executed is a decision which influences how you see things. As /u/elos_ has shown, if you look at what the plan was intended for you get a different picture. If you look at how other countries used these type of plans, you get a different picture. This picture is constructed by historians. Other pictures can be constructed using more (or less) information. There is no "correct" picture, but there are more and less nuanced pictures. Suffice to say, the picture you're presenting here is not very nuanced.

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Sources:

• Peter Burke, History and Social Theory 2nd edition (Cambridge 2005)
• Paul Ricoeur, Time and Narrative Volume 3 (Chicago 1988)
• John Tosh, The Pursuit of History Revised 3rd edition (London 2002)

Are you asking a question here, or looking to debate a position? If the latter, this is not the correct subreddit, and you should consider reposting this to /r/history instead.